Their press release via Media Matters:
MailChimp doesn’t generally comment on individual users or accounts, but we’ll make an exception today.
MailChimp notified Infowars that their accounts have been terminated for violating our Terms of Service, which make it clear that we don’t allow people to use our platform to disseminate hateful content.
We take our responsibility to our customers and employees seriously. The decision to terminate this account was thoughtfully considered and is in line with our company’s values.
NOTE: MailChimp runs the JMG newsletter.